In this paper, the problem of resource allocation in OFDM based decode-and-forward (DF) cognitive radio (CR) system is considered. The objective is to maximize the CR system throughput by optimizing the subcarrier pairs and powers. The interference introduced to the primary system should not exceed the prescribed interference temperature limit. The resources are optimized jointly by applying the dual decomposition technique to get asymptotically optimal solution. In addition, a suboptimal algorithm that performs the resources allocation in two phases is proposed. By the suboptimal algorithm, the subcarrier pairing is first performed considering the channels quality as well as the interference introduced to the primary system. Afterwards, the powers are allocated in the second phase by applying a waterfilling-like algorithm. The suboptimal algorithm reduces significantly the computational complexity with small performance degradation. The simulation results confirm the efficiency of the proposed algorithm.
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